When fillet welding of a corner of metallic plates is carried out by running the carriage mounted with the welding torch, the traveling direction of the carriage should be controlled so that the welding torch may travel along the welding line.
FIG. 14 illustrates an example of the conventional tracking welders. In a case of fillet welding of the corner made by a virtually horizontally placed steel plate (a) and a steel web plate (b) erected on the steel (a), a self-travelable carriage (d) mounted with a welding torch (c) is placed on the steel plate (a), and the welding of the corner is automatically performed with the welding torch (c) at the same time of running the carriage (d) along a tracking face, that is the web plate (b).
The carriage (d) is mounted with a front tracking roller (e) projecting toward the tracking face (the web plate) (b) and a rear tracking roller (f) projecting at a long distance as compared with the front tracking roller e, and by running the carriage (d) in direction (g) slightly inclined toward the tracking face (the web plate) (b), the front tracking roller (e) and the rear tracking roller (1) become to be always contact with the tracking face (the web plate) (b), and thus a distance between the welding torch (c) and the corner is kept constant.
However, as for the above-mentioned conventional tracking welder, while it is possible to automatically weld the corner between the horizontally placed steel plate (a) and the web plate (b), there is a problem in that such the machine is not available in a case the web plate (b) does not exist (in a case of butt welding, for example).
Moreover, even when welding the corner by utilizing the erected wall (b), there still remains a problem of limitation in the traveling directions of the carriage (d), and it is impossible to perform welding by running the carriage in the reverse direction from the arrow (g).
Furthermore, since the carriage (d) gradually approaches the web plate (b) while traveling, the wheels of the carriage (d) tend to be pushed back by the tracking rollers (e) and (f), and always slip in the lateral direction, thereby causing the strong frictional resistance and making the carriage (d) not to travel so smoothly. Further, since the two tracking rollers (e) and (f) press the web plate (b) while the carriage (d) is traveling, there is another problem of a danger in that the web plate (b) pushed by the rollers (e) and (f) might come off from the steel plate (a) in a case where the web plate (b) is temporally tacked on the steel plate (a), and it becomes subject to solve these problems.